Momentum Distributions Of Charged Particles Research Articles

Pseudorapidity dependence of the transverse momentum distribution of charged particles in [formula omitted] collisions at 0.9, 2.36, and 7 TeV

We study the transverse momentum spectra of charged particles from 0.1−2 GeV/c in bins of pseudorapidity η of width 0.2 ranging from 0 to 2.4 produced in pp collisions, at three different center of mass energies, namely s=0.9, 2.36, 7TeV. We used PYTHIA8.307 and QGSJETII-04 and compared the simulation results with experimental data under the same conditions. The PYTHIA8 model has an excellent description of the experimental data, particularly at the high pT region of the distribution, and the prediction is independent of the η ranges. Furthermore, the predictions are more or less the same at lower values of pT, but a more prominent bump is observed for 0.4≤pT≤0.8GeV/c with increasing the center-of-mass energy. The QGSJET model reproduces the data only in the intermediate region of the pT over all the η slices and underpredicts for low and high pT regions. With the increase in the center of mass energy, the model’s predictions got closer to the data, particularly at a high part of the pT distributions. Furthermore, the Blast wave model with Tsallis statistics is applied to the pT spectra of CMS data and PYTHIA8 and QGSJET models, and the kinetic freeze-out temperature, transverse flow velocity, and the entropy parameter q are extracted. The kinetic freeze-out temperature increases from lower pseudorapidity regions to higher pseudo-rapidity regions. Transverse flow velocity and the entropy parameter q have the opposite trend to kinetic freeze-out temperature. All these parameters are also more significant at 7TeV and have the lowest values at 0.9TeV, which shows the dependence of these parameters on the collision energy.

Measurement of angular and momentum distributions of charged particles within and around jets with the ATLAS detector

Studies of jet fragmentation in heavy-ion collisions can provide information about the mechanism of jet quenching inside the hot and dense QCD matter created in these collisions. These proceedings present results from measurements of charged particle yields within and around the jets in dijet, gamma+jet and Z+jet systems measured in $5.02$~TeV Pb+Pb and $pp$ collisions using the ATLAS detector at the LHC.

A Composite Velocity Map Imaging Spectrometer for Ions and 1 keV Electrons at the Shanghai Soft X-ray Free-Electron Laser

Velocity map imaging (VMI) spectrometry is widely used to measure the momentum distribution of charged particles with the kinetic energy of a few tens of electronVolts. With the progress of femtosecond laser and X-ray free-electron laser, it becomes increasingly important to extend the electron kinetic energy to 1 keV. Here, we report on a recently built composite VMI spectrometer at the Shanghai soft X-ray free-electron laser, which can measure ion images and high-energy electron images simultaneously. In the SIMION simulation, we extended the electron kinetic energy to 1 keV with a resolution <2% while measuring the ions with the kinetic energy of 20 eV. The experimental performance is tested by measuring Ar 2p photoelectron spectra at Shanghai Synchrotron Radiation Facility, and O+ kinetic energy spectrum from dissociative ionization of O2 by 800 nm femtosecond laser. We reached a resolution of 1.5% at the electron kinetic energy of 500 eV. When the electron arm is set for 100 eV, a resolution of 4% is reached at the ion kinetic energy of 5.6 eV. This composite VMI spectrometer will support the experiment, such as X-ray multi-photon excitation/ionization, Auger electrons emission, attosecond streaking.

Study of transverse momentum and nuclear modification factors distribution of charged particles produced in pp and Pb–Pb collisions at s NN = 2.76TeV and 5.02TeV

We have studied transverse momentum distributions of charged particles produced in pp and Pb–Pb collisions at [Formula: see text] TeV and 5.02 TeV in the pseudorapidity interval [Formula: see text] and transverse momentum range [Formula: see text][Formula: see text]GeV/[Formula: see text]. We simulated data using EPOS-LHC, EPOS-1.99 and QGSJETII-04 models. The simulation data is compared with the ALICE experimental data values at [Formula: see text] TeV and 5.02 TeV for pp and most central Pb–Pb collisions. It has been observed that, EPOS-LHC and QGSJETII-04 models explain the experimental results for pp collision at [Formula: see text] TeV and 5.02 TeV. The behavior of nuclear modification factors has been studied. The simulation codes of all three models EPOS-LHC, EPOS-1.99 and QGSJETII-04 overestimate the experimental results at low transverse momentum interval: [Formula: see text] GeV/[Formula: see text], for Pb–Pb collisions at [Formula: see text] TeV and 5.02 TeV. However, only EPOS-LHC model can explain the experimental data at high transverse momentum in the range: [Formula: see text] GeV/[Formula: see text]. EPOS-1.99 and QGSJETII-04 underestimate in the region of Cronin effect and cannot give satisfactory estimates for the [Formula: see text] values for which [Formula: see text] demonstrates stronger suppression because of the collective parton effect. It can be inferred that these effects are not taken into account in EPOS-1.99 and QGSJETII-04 models. These models, however, satisfactorily explain the ALICE experimental data in the ranges of [Formula: see text] for which nuclear modification factor [Formula: see text] shows rising trend.

Non-extensive transverse momentum distribution for identified particles at SNN = 7.7, 11.5, 19.6, 27, 39GeV

The transverse momentum distribution of charged particles formed in Au–Au collisions at Beam Energy Scan (BES) ([Formula: see text][Formula: see text]GeV) is investigated. In addition, [Formula: see text] spectra of [Formula: see text] particle at [Formula: see text][Formula: see text]GeV were examined. Tsallis distribution is used to extract the temperature, volume and the entropic index from the experimental results at mid-rapidity and zero chemical potential. We measure some particle ratios like [Formula: see text] and [Formula: see text] which are puzzling horn in the experiment and in the thermal model. We conclude that the horn vanished when we used Tsallis distribution, but this does not confirm a solution to the puzzle, which is primarily visible in the experimental results.

Strangeness enhancement due to string fluctuations

We study string fragmentation in high multiplicity proton-proton collisions in a model where the string tension fluctuates. These fluctuations produce exponential pion spectra which are fitted to the transverse momentum distributions of charged particles for different multiplicities. For each multiplicity the so obtained hadronic slope parameter defines the magnitude of the string fluctuations which in turn determines the produced ratio of strange to light quarks. PYTHIA string decay simulations are used to convert each ratio of strange to light quarks to the appropriate ratio of strange hadrons to pions.

Investigation of Particle Distributions in Xe-Xe Collision at sNN=5.44 TeV with the Tsallis Statistics

The distribution characteristic of final-state particles is one of the significant parts in high-energy nuclear collisions. The transverse momentum distribution of charged particles carries essential evolution information about the collision system. The Tsallis statistics is used to investigate the transverse momentum distribution of charged particles produced in Xe-Xe collisions at sNN=5.44 TeV. On this basis, we reproduce the nuclear modification factor of the charged particles. The calculated results agree approximately with the experimental data measured by the ALICE Collaboration.

Measurement of angular and momentum distributions of charged particles within and around jets in Pb+Pb and pp collisions at sNN=5.02 TeV with the ATLAS detector

Studies of the fragmentation of jets into charged particles in heavy-ion collisions can provide information about the mechanism of jet-quenching by the hot and dense QCD matter created in such collisions, the quark-gluon plasma. This paper presents a measurement of the angular distribution of charged particles around the jet axis in $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV Pb+Pb and $pp$ collisions, using the ATLAS detector at the LHC. The Pb+Pb and $pp$ data sets have integrated luminosities of 0.49 nb$^{-1}$ and 25 pb$^{-1}$, respectively. The measurement is performed for jets reconstructed with the anti-$k_{t}$ algorithm with radius parameter $R = 0.4$ and is extended to an angular distance of $r= 0.8$ from the jet axis. Results are presented as a function of Pb+Pb collision centrality and distance from the jet axis for charged particles with transverse momenta in the 1$-$63 GeV range, matched to jets with transverse momenta in the 126$-$316 GeV range and an absolute value of jet rapidity of less than 1.7. Modifications to the measured distributions are quantified by taking a ratio to the measurements in $pp$ collisions. Yields of charged particles with transverse momenta below 4 GeV are observed to be increasingly enhanced as a function of angular distance from the jet axis, reaching a maximum at $r=0.6$. Charged particles with transverse momenta above 4 GeV have an enhanced yield in Pb+Pb collisions in the jet core for angular distances up to $r = 0.05$ from the jet axis, with a suppression at larger distances.

Analysis of transverse momentum distributions of charged particles produced in CC interactions at 4.2 A GeV/c

In this paper, the transverse momentum and maximum transverse momentum distributions of protons and pions produced in an event for CC collisions at 4.2 A GeV/c have been analyzed. This analysis is based on experimental data obtained from 2 m propane bubble chamber at Joint Institute for Nuclear Research, Dubna, Russia and simulation data obtained from Dubna cascade code. We observed three disparate zones for the transverse momentum distribution of the produced particles. The third zone where transverse momentum is greater than 0.375 GeV/c is restricted only for pions with transverse momentum approximately equal to 1 GeV/c, and for protons the restricted value of [Formula: see text] is [Formula: see text][Formula: see text]1.5 GeV/c. So contribution of pions to this region is less and decreases sharply than the contribution of protons. The results of cascade model are not fully compatible with the experimental results in the third [Formula: see text] region, as this region contains less number of particles for model data as compared with experimental data but is compatible in the case of [Formula: see text].

Measurement of angular and momentum distributions of charged particles within and around jets in Pb+Pb and pp collisions at [formula omitted] with ATLAS at the LHC

Studies of the fragmentation of jets into charged particles in heavy-ion collisions can help in understanding the mechanism of jet quenching by the hot and dense QCD matter created in such collisions, the quark-gluon plasma. These proceedings present a measurement of the angular distribution of charged particles around the jet axis in sNN=5.02TeV Pb+Pb and pp collisions, done using the ATLAS detector at the LHC. The measurement is performed inside jets reconstructed with the anti-kt algorithm with radius parameter R=0.4, and is extended to regions outside the jet cone. Results are presented as a function of Pb+Pb collision centrality, and both jet and charged-particle transverse momenta.

Study of Pseudorapidity and Transverse-Momentum Distributions of Charged Particles in pp Interactions at √s = 13 TeV Using Hadron Production Models

Pseudorapidity (η) and Transverse momentum (pT) distributions of charged particles produced in proton-proton (pp) collisions at √s = 13 TeV are studied. Transverse momentum distributions of charged particles are considered in the Pseudorapidity region of |η| < 0.8 and in the transverse momentum range of 0 < pT < 20 GeV/c. EPOS1.99, EPOS-LHC and QGSJETII-04 models are used to perform simulations. In order to check the validity of simulations performed using these Monte-Carlo event generators, the results are compared to the measurements of ALICE experiment at the LHC CERN. For the pT distribution, the EPOS1.99 and QGSJET underpredict the experimental data while the EPOS-LHC model reproduced the distribution very well. EPOS-LHC model describes the experimental data very well as compared to the other two models for the ratio of pT spectra of charged particles at √s = 13 TeV to 7 TeV. EPOS-LHC also describes the pseudorapidity distribution very well while the EPOS 1.99 and QGSJETII-04 underpredict and overpredict the distribution respectively.

Measurements of Ω− branching fractions

Using $e^+e^-$ annihilation data taken at the CESR collider with the CLEO-c detector, measurements of two main $\Omega^-$ branching fractions have been made using the reaction $\psi(2S)\to\Omega^-\overline{\Omega}^+$, hyperon pair production at $\sqrt{s}=3.69$~GeV, the peak of the $\psi(2S)$ resonance. $\Omega^-$ decay channels are identified through momentum distributions of charged particles, and systematics of the $\Omega^-$ branching fractions have been studied. The result gives: $\mathcal{B}(\Omega^- \to \Lambda^0 K^-) = (68.9\pm9.5\pm4.3)\%$, and $ \mathcal{B}(\Omega^- \to \Xi^0 \pi^-) = (19.0\pm4.0\pm1.2)\%$.

Transverse Momentum Distributions of Charged Particles Produced in Deuteron-Carbon Interactions at 4.2A GeV/c

In this work, the behavior of transverse momentum (pT) and maximum pT (pTmax) distribution of light-flavored hadrons, produced in deuteron-carbon (dC) interactions at 4.2A GeV/c, is presented. We use the data, provided by the Laboratory of High Energy (LHE) with propane bubble chamber of 2 m of the Joint Institute for Nuclear Research (JINR), Dubna Russia. The results of the experimental data are compared with the predictions of the cascade model, Dubna version. Three regions in terms of the pT-distributions trend are observed for all types of particles, where pT ∼ 1 and 1.5 GeV/c are the limiting values for pions and protons, respectively, in the region-III, for which the pT > 0.375 GeV/c. The protons’ contribution to this region is an order of magnitude more than of the mesons and the distribution of the latter decreases faster than of the former. The model cannot predict the experimental results in the region-III, completely, where the number of particles is less than in the experiment.

A Description of the Transverse Momentum Distributions of Charged Particles Produced in Heavy Ion Collisions at RHIC and LHC Energies

By assuming the existence of memory effects and long-range interactions, nonextensive statistics together with relativistic hydrodynamics including phase transition are used to discuss the transverse momentum distributions of charged particles produced in heavy ion collisions. It is shown that the combined contributions from nonextensive statistics and hydrodynamics can give a good description of the experimental data in Au+Au collisions at sNN=200 GeV and in Pb+Pb collisions at sNN=2.76 TeV for π± and K± in the whole measured transverse momentum region and for pp- in the region of pT≤2.0 GeV/c. This is different from our previous work using the conventional statistics plus hydrodynamics, where the describable region is only limited in pT≤1.1 GeV/c.

Momentum distribution of charged particles in jets in dijet events and comparison to perturbative QCD predictions

Inclusive momentum distributions of charged particles are measured in dijet events. Events were produced at the AMY detector with a centre of mass energy of 60 GeV. Our results were compared, on the one hand to those obtained from other e+e−, ep as well as CDF data, and on the other hand to the perturbative QCD calculations carried out in the framework of the modified leading log approximation (MLLA) and assuming local parton–hadron duality (LPHD). A fit of the shape of the distributions yields Qeff = 263±13 MeV for the AMY data. In addition, a fit to the evolution of the peak position with dijet mass using all data from different experiments gives Qeff = 226±18 MeV. Next, αs was extracted using the shape of the distribution at the Z0 scale, with a value of 0.118 ± 0.013. This is consistent, within the statistical errors, with many accurate measurements. We conclude that it is the success of LPHD + MLLA that the extracted value of αs is correct. Possible explanations for all these features will be presented in this paper.

Charged-particle distributions in pp interactions at [Formula: see text] measured with the ATLAS detector.

This paper presents measurements of distributions of charged particles which are produced in proton–proton collisions at a centre-of-mass energy of sqrt{s} = 8 mathrm {, TeV} and recorded by the ATLAS detector at the LHC. A special dataset recorded in 2012 with a small number of interactions per beam crossing (below 0.004) and corresponding to an integrated luminosity of 160 upmu mathrm{b}^{-1} was used. A minimum-bias trigger was utilised to select a data sample of more than 9 million collision events. The multiplicity, pseudorapidity, and transverse momentum distributions of charged particles are shown in different regions of kinematics and charged-particle multiplicity, including measurements of final states at high multiplicity. The results are corrected for detector effects and are compared to the predictions of various Monte Carlo event generator models which simulate the full hadronic final state.

The Tsallis distribution at large transverse momenta

Fits to the transverse momentum distributions of charged particles produced in p - p collisions at LHC energies based on the Tsallis distribution have been shown to work over 14 orders of magnitude. Two versions of the Tsallis distribution are compared and discussed, the thermodynamically consistent version leads to a temperature of T = 74 +/- 13 MeV at the highest beam energy, a result which is in agreement with previous analyses done with lower transverse momentum data.

Interpretation of charged-particle spectra inp+pandp+Pbcollisions at energies available at the CERN Large Hadron Collider using an improved hijing code with a collective cascade

We supplement the Heavy Ion Jet Interaction Generator (hijing) code with a collective cascade recipe and updated Martin-Stirling-Thorne-Watt (MSTW2009) parton distribution functions (PDFs) to describe nonsingle diffractive (NSD) $p+p$ and Pb collisions at CERN Large Hadron Collider energies. The collective cascade, developed in the space of an impact parameter, is used to induce nuclear modification of nucleons, that are involved in primary interactions, inside the dense nuclear medium. It is found that the improved hijing (Imhijing) code (that with MSTW2009 PDFs) reproduces rather well the pseudorapidity density, the multiplicity, and the transverse momentum distributions of charged particles within the pseudorapidity interval $|{\ensuremath{\eta}}_{\mathrm{c}.\mathrm{m}.\mathrm{system}}|&lt;2.4$ in NSD $p+p$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=0.9$, 2.36, and 7 TeV. The Imhijing with collective cascade calculations is also shown to be a good fit to the pseudorapidity density (in the laboratory system) and transverse momentum $({p}_{T})$ dependence of the nuclear modification of charged particles in NSD $p+\mathrm{Pb}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=5.02\phantom{\rule{4pt}{0ex}}\mathrm{TeV}$. The effects of the collective cascade are clearly seen in the target $(3&lt;{\ensuremath{\eta}}_{\mathrm{lab}}&lt;4)$ and central (within $|{\ensuremath{\eta}}_{\mathrm{c}.\mathrm{m}.\mathrm{system}}|&lt;0.3$ at $1&lt;{p}_{T}&lt;8\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}/\phantom{\rule{0.0pt}{0ex}}c)$ interaction regions when studying the pseudorapidity density and transverse momentum dependence of the nuclear modification factor of the charged particles, respectively.

Transverse momentum distributions in proton–proton collisions at LHC energies and Tsallis thermodynamics

A detailed study of the transverse momentum distributions of charged particles produced in p–p collisions at large hadron collider energies is presented. This is done using a thermodynamically consistent form of the Tsallis distribution. All variables used are thermodynamical and in particular, the temperature, T, follows from the standard thermodynamic definition as being the derivative of the energy with respect to the (Tsallis) entropy. The momentum distribution of the final state particles can be described very well by the Tsallis distribution. The values of the parameters are determined from measurements by the ALICE, ATLAS and CMS collaborations and are discussed in detail. In particular, the Tsallis parameter, q, is found with consistent values for all the transverse momentum distributions despite large differences in kinematic regions and shows a slight increase with beam energy, reaching a value of 1.15 at 7 TeV. It is concluded that the hadronic system created in high-energy p–p collisions at mid-rapidity is consistent with Tsallis thermodynamics.

Chemical Potentials of Quarks Extracted from Particle Transverse Momentum Distributions in Heavy Ion Collisions at RHIC Energies

In the framework of a multisource thermal model, the transverse momentum distributions of charged particles produced in nucleus-nucleus (A-A) and deuteron-nucleus (d-A) collisions at relativistic heavy ion collider (RHIC) energies are investigated by a two-component revised Boltzmann distribution. The calculated results are in agreement with the PHENIX experimental data. It is found that the source temperature increases obviously with increase of the particle mass and incident energy, but it does not show an obvious change with the collision centrality. Then, the values of chemical potentials for up, down, and strange quarks can be obtained from the antiparticle to particle yield ratios in a wide transverse momentum range. The relationship between the chemical potentials of quarks and the transverse momentum with different centralities is investigated, too.